LTC1419AIG データシートの表示（PDF） - Linear Technology
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LTC1419AIG Datasheet PDF : 20 Pages
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LTC1419
APPLICATIONS INFORMATION
frequencies outside the fundamental. Figure 2 shows a
typical LTC1419 FFT plot.
0
fSAMPLE = 800kHz
– 20
fIN = 99.804687kHz
SFDR = 98dB
THD = –93.3dB
– 40
– 60
– 80
–100
–120
–140
0 50 100 150 200 250 300 350 400
FREQUENCY (kHz)
1419 F02a
Figure 2a. LTC1419 Nonaveraged, 4096 Point FFT,
Input Frequency = 100kHz
0
fSAMPLE = 800kHz
– 20 fIN = 375kHz
SFDR = 88.3dB
SINAD = 80.1
– 40
– 60
– 80
–100
–120
–140
0 50 100 150 200 250 300 350 400
FREQUENCY (kHz)
1419 F02b
Figure 2b. LTC1419 Nonaveraged, 4096 Point FFT,
Input Frequency = 375kHz
Signal-to-Noise Ratio
The signal-to-noise plus distortion ratio [S/(N + D)] is the
ratio between the RMS amplitude of the fundamental input
frequency to the RMS amplitude of all other frequency
components at the A/D output. The output is band limited
to frequencies from above DC and below half the sampling
frequency. Figure 2 shows a typical spectral content with
a 800kHz sampling rate and a 100kHz input. The dynamic
performance is excellent for input frequencies up to and
beyond the Nyquist limit of 400kHz.
8
Effective Number of Bits
The effective number of bits (ENOBs) is a measurement of
the resolution of an ADC and is directly related to the
S/(N + D) by the equation:
N = [S/(N + D) – 1.76]/6.02
where N is the effective number of bits of resolution and
S/(N + D) is expressed in dB. At the maximum sampling
rate of 800kHz, the LTC1419 maintains near ideal ENOBs
up to the Nyquist input frequency of 400kHz (refer to
Figure 3).
14
13
12
11
10
9
8
7
6
5
4
3 fSAMPLE = 800kHz
2
1k
10k
100k
INPUT FREQUENCY (Hz)
86
80
74
68
62
1M 2M
1419 TA02
Figure 3. Effective Bits and Signal/(Noise + Distortion)
vs Input Frequency
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
sum of all harmonics of the input signal to the fundamental
itself. The out-of-band harmonics alias into the frequency
band between DC and half the sampling frequency. THD is
expressed as:
THD = 20Log V22 + V32 + V42 + …Vn2
V1
where V1 is the RMS amplitude of the fundamental fre-
quency and V2 through Vn are the amplitudes of the
second through nth harmonics. THD vs Input Frequency is
shown in Figure 4. The LTC1419 has good distortion
performance up to the Nyquist frequency and beyond.
1419fb
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